Non-isolated power conversion system having multiple switching power converters

Abstract

A non-isolated power conversion system has an input stage and an output stage. A plurality of cascaded switching power converter stages are coupled between the input stage and the output stage. Each of the plurality of switching power converter stages has at least one switch that is activated in accordance with a duty cycle associated with a switching cycle. At least one energy storage device temporarily stores energy that is proportional to the duty cycle during the switching cycle for delivery to the output stage.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention generally relates to power conversion systems, more particularly to non-isolated power conversion systems that use multiple switching power converters. [0003] 2. Description of the Prior Art [0004] Isolated and non-isolated power conversion systems are known. Isolated power supplies generally use a transformer for isolating an input power stage from an output power stage through primary and secondary windings. Non-isolated power conversion systems usually use cascaded switching power converter stages associated with one or more switching cycles. [0005] Known non-isolated power converters have been used in AC-DC, AC-AC, DC-AC, and DC-DC applications. Examples of such converters include buck converters, boost converter and buck-boost converters that can be implemented using various switching power conversion topologies. In such topologies, the input / output conversion ratios are determined according to d...

AI Technical Summary

Benefits of technology

The present invention provides non-isolated multi-stage switching power converters that provide high conversion ratios in response to the duty cycle associated with a switching cycle of cascaded power converters. The converters have a power conversion ratio less than or equal to one for step-down power converters and greater than or equal to one for step-up power converters. The system operates with larger duty cycle that produces wider switch activation control signals applied to switches that lower voltage stresses and reduce switching losses for step-down power converters, or with smaller duty cycle that reduces switch conduction losses for step-up power converters. The system includes an input stage and an output stage with a plurality of cascaded switching power converter stages that have at least one switch activated in accordance with the duty cycle associated with the switching cycle. The energy storage device stores energy that is proportional to the duty cycle during the switching cycle for delivery to the output stage. The system also includes at least one energy storage device connected to adjacent switching power converter stages, a junction point between switches on adjacent stages, and multiple pairs of switches, inductors, and energy storage devices arranged in parallel for each stage. The power conversion ratio of the system can be greater than one or alternatively less than or equal to one, and the voltage of the energy storage device can be related to the input voltage or the output voltage and the duty cycle. The circuits of the invention can be implemented in various ways, such as connecting multiple pairs of switches, diode rectifiers, and capacitors in parallel or for high current applications.

Problems solved by technology

Because the duty cycle of the conventional buck converter is proportional to the conversion ratio of input / output voltage in applications that use high switching frequencies for providing high conversion ratios, the turn-on periods of the switches are extremely short.

Consequently, extremely narrow switch activation pulses are necessary for maintaining very short duty cycles.

Generating very narrow turn-on switch activation control signals, however, is difficult because of parasitic components that are associated with the switching devices and the switch activation circuit.

In addition, a conventional buck converter in applications that require a high-voltage conversion ratio suffers from a serious efficiency degradation.

Usually, high-voltage switching devices are more expensive and have greater conduction losses in comparison with low-voltage-rated switching devices.

The efficiency of the conventional buck converter is further degraded by a severe switching loss.

Because the duty cycle of the conventional boost converter should be maximized to provide a very large conversion ratio of input / output voltage, the turn-on periods of the switches are extremely long.

Consequently, extremely long switch conduction period increases conduction losses and lowers converter efficiency.

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